Method for producing an assembly

ABSTRACT

The invention relates to a method for producing an assembly ( 1 ) consisting at least of a first component ( 2 ) and a second component ( 3 ), the first component ( 2 ) being arranged at least partly inside the second component ( 3 ), and the first component ( 2 ) and the second component ( 3 ) being produced from at least one metal sintering powder according to a sintering method comprising the steps of powder pressing and sintering. The first component ( 2 ) and the second component ( 3 ) consisting of the at least one metal sintering powder are pressed together in a mold to form a one-piece green compact ( 4 ) and the two components ( 2, 3 ) are only separated after sintering.

The invention relates to a method for producing an assembly consisting at least of a first component and a second component, wherein the first component is arranged at least partly inside the second component, wherein the first component and the second component are produced from at least one metal sintering powder according to a sintering method comprising the steps of powder pressing and sintering.

The invention also relates to a press mold for producing a green compact for an assembly consisting at least of a first component and a second component, with a mold cavity for holding at least one sintering powder and a pressing punch.

The production of metal components by means of powder metallurgy has been known for a long time. An essential advantage of this technique is that complicated geometric component shapes can be produced more easily in this way, as no or only a small amount of machining is necessary after the sintering. For this reason sintered components are widespread and are used for many different assemblies.

The objective of the present invention is to make it possible to simplify the powder metallurgical production of a metal assembly made from at least two components.

Said objective is achieved by means of the aforementioned method, in which the first component and the second component made of at least one metal sintering powder are compacted together in a mold to form a one-piece green compact and the two components are only separated after the sintering. Furthermore, the objective is achieved by the aforementioned press mold, in which the mold cavity comprises a first mold cavity for the first component and a second mold cavity for the second component, wherein the first mold cavity is separated from the second mold cavity by at least one mold wall, and wherein also the first mold cavity is at least partly surrounded by the second mold cavity, and in the mold wall separating the first mold cavity from the second mold cavity at least one opening is formed, by means of which the first mold cavity is connected to the second mold cavity, or alternatively in a base area of the mold cavity and/or in the pressing punch at least one depression is formed, by means of which the first mold cavity is connected to the second mold cavity.

It is an advantage that the two components can be produced together and are only separated after the sintering. In this way both the pressing and sintering times are shortened. In addition, in this way a second press mold is not necessary for the second component. Furthermore, the occupancy of the sintering furnace can be improved in that the two components do not need to be sintered separately. The space available in the sintering furnace is thus better used, whereby lastly it is also possible to reduce the cost of the energy required for operating the sintering furnace. By producing the two components together until after the sintering the throughput time for the production of the assembly can also be reduced considerably, thereby also achieving a considerable reduction of the cost. It is an advantage with respect to the press molds that the latter can be configured to be relatively simple despite the connection of the two components, in that to form the connection only at least one depression or at least one opening has to be provided.

According to a preferred embodiment variant of the method the first component can be connected to the second component by at least one predetermined breaking point. A predetermined breaking point is defined within the meaning of the invention to be an area in which the two components are separated after sintering. The predetermined breaking point can therefore also be denoted as a designated separating point. The predetermined breaking point is not necessarily a tapered area or notched area. By forming the connection as a predetermined breaking point the separation of the two components is simplified after sintering and in this way a defined area can be provided in which the two components are to be separated.

It is an advantage if the predetermined breaking point is configured as at least one web. The web can be easily represented by powder metallurgy and improves the cohesion of the two components during production. In addition, the web can easily be removed again after sintering.

According to one embodiment variant it is also possible that the at least one web is formed between an outer surface of the first component and an inner surface of the second component. In this way this “weak point” can be protected more effectively from external mechanical influences.

It is also an advantage if the web is formed off-center and in the region of an end face of the first component and the second component, as in this configuration the accessibility of the web can be improved for later separation. In addition the press mold can be also be produced more easily in this way.

To achieve a better distribution of force and pressure during production a plurality of webs can be arranged distributed evenly over the periphery of the first component. This also has the advantage that the first, inner component is less prone to warping during the sintering, as it is supported by the second, outer component. For this reason the plurality of webs are preferably formed at the same height.

It is also possible alternatively or additionally to the aforementioned type of connection that the first component and the second component are joined together on the end faces. On the one hand, this has the advantage, that the mold cavity of the press mold can be designed more simply, in that the connection is placed in the edge area of the mold cavity. On the other hand however, in this way the separation of the two components can also be simplified after sintering, as the two components can be separated at the same time, i.e. jointly, by machining.

Preferably the first component is produced coaxially to the second component, so that no uneven or varying forces act on the first, inner component.

The components can be separated by breaking or by piercing or by turning, but piercing and turning are preferable, as in this way the separation can be more predictable and cut-outs are easier to avoid on one of the two components.

In the preferred embodiment variant of the invention the first component is produced as a rotor and the second component as a stator of a pump.

It is also possible that the first component is made from a first sintering powder and the second component is made from a second sintering powder, wherein the first sintering powder has a different composition from the second sintering powder. It is thus possible in only a single method step to compress two components with different, mechanical properties and then sinter them jointly.

For a better understanding of the invention the latter is explained in more detail with reference to the accompanying Figures.

In a simplified, schematic representation:

FIG. 1 is an assembly consisting of at least two metal components in an oblique view;

FIG. 2 is a first embodiment variant of a green compact for producing a sintered component;

FIG. 3 is a second embodiment variant of a green compact for producing a sintered assembly;

FIG. 4 is a section of a first embodiment variant of a press mold;

FIG. 5 is a section of a second embodiment variant of a press mold.

First of all, it should be noted that in the variously described exemplary embodiments the same parts have been given the same reference numerals and the same component names, whereby the disclosures contained throughout the entire description can be applied to the same parts with the same reference numerals and same component names. Also details relating to position used in the description, such as e.g. top, bottom, side etc. relate to the currently described and represented figure and in case of a change in position should be adjusted to the new position.

The invention relates to a powder metallurgy method for producing an assembly 1, as shown by way of example in FIG. 1 in an oblique view.

Powder metallurgical methods of this kind are already known from the prior art. Usually these methods comprise the following method steps:

-   -   providing the powder, possibly preparing a powder mixture;     -   pressing the powder into a green compact;     -   dewaxing if necessary;     -   sintering the green compact;     -   if necessary subsequently pressing/calibrating the sintered         component,     -   if necessary mechanically post-processing the sintered         component.

Alternatively, the sintering can be performed in two steps, whereby in a first step the green compact is sintered into a brown compact and the latter is then finally sintered by means of high temperature sintering.

As said methods and the method parameters used and the metal powder (mixtures) used therein are known, reference is made to the relevant prior art to avoid repetition.

The assembly 1 consists of at least one first component 2 and a second component 3. In FIG. 1 a preferred embodiment variant of the assembly 1 is shown by way of example. The first component 2 forms the rotor and the second component 3 forms the stator of a pump, in particular a vane pump. The vanes, which are inserted into the shown slots as is generally known, are not shown. It is thus clear that the assembly 1 can also comprise more than two components 2, 3.

In general, the first component 2 of the assembly 1 produced according to the method of the invention can be arranged at least partly inside the second component 3. The first component 2 can therefore also be referred to as an inner component and the second component 3 can also be referred to as an outer component.

Therefore, in addition to the embodiment variant of the assembly 1 as a vane pump the assembly 1 can also be a VVT group, a so-called decoupled gear, in which an inner gear part is connected by a rubber ring to an outer gear part bearing the toothing etc. In general, the assembly 1 can be an assembly which comprises an inner component which is surrounded peripherally by an outer component.

The term “at least partly” means in this case that the first component 2, as shown in FIG. 1, need not be completely surrounded by the second component 3, but additional components, such as e.g. covers, can be provided to form an inner chamber in which the first component 2 is mounted.

The first and the second component 2, 3 are produced from a metal sintering powder, for example a steel powder, as already explained above. In addition, a green compact 4 is produced from the sintering powder prior to sintering.

In FIG. 2 a first preferred embodiment variant of the green compact 4 is shown. The green compact 4 consists in the shown embodiment variant of a first green compact component 5, from which the first component 2 is produced, and a second green compact component 6, from which the second component 3 is produced. According to the above explanations the second green compact component 6 surrounds first green compact component 5 at least partly.

The two green compact components 5, 6, as is usual in sintering methods, already have the geometry of the two finished components 2, 3. However, a change in the dimensions needs to be taken into account during the sintering itself, as known by a person skilled in the art. For this reason therefore in the invention the terms “component” and “green compact component” can be used synonymously, as they only differ from one another essentially in terms of when they are formed in the sequence of the method.

It is essential for the method for producing the assembly 1 that the first green compact component 5 is connected to the second green compact component 6 and remains connected until after the sintering. For this purpose the first green compact component 5 and the second green compact component 6 are pressed from the sintering powder in a common press mold 7 (FIG. 4).

To connect the first green compact component 5 to the second green compact component 6 a predetermined breaking point can be produced in said press mold 7. Said predetermined breaking point can be formed according to a preferred embodiment variant by at least one web 8.

In the embodiment variant of the green compact 4 shown in FIG. 2 a plurality of webs are formed. In particular four webs 8 are provided. However, this number should not be seen to be restrictive in terms of the invention. Rather, fewer or more than four webs 8 can also be produced, for example two, three, five, six, etc.

The web 8 can be configured as an annular web which runs continuously over the entire circumference of the first, inner green compact component 5. However, as in the shown example of the assembly 1 the first green compacts component 5 comprises slit-like recesses 9 for receiving the aforementioned vanes, which extend up to an outer surface 10 (casing surface) of the first green compact component 5, the web 8 is preferably interrupted in the region of said recesses 9. In other words, to connect the first green compact component 5 to the second green compact component 6 a plurality of webs 8 are formed which are formed or arranged on the outer surface 10, preferably distributed uniformly around the periphery 11 of the first green compact component 5, in particular distributed evenly.

However, it is also possible, as shown by the bottom right web 8 in FIG. 2, that the web or web(s) 8 also extend over the recess(es) 9 in the outer surface 10 of the first green compact component 5. In this case it is an advantage, if the recess(es) 9 continue into the web or webs 8, so that the web or the webs 8 have a tapering 12 in the area of said recesses 9, or in other words after the two green compact components 5, 6 have been joined together the recess(es) 9 have an outwardly widening cross section. In this way it is possible to prevent cut-outs during the subsequent separation of the two components 2, 3 in the region of the sensitive edges and the mechanical process of removing the webs 8 after separating the two components 2, 3 is easier to perform.

The web or webs 8 are preferably formed between the outer surface 10 of the first green compact component 5 and an inner surface 13 of the second green compact component 6. The inner surface 13 of the second green compact component 6 is arranged to be adjacent to the outer surface 10 of the first green compact component 5.

Furthermore, it is preferable if the at least one web 8 is arranged to be off-center in relation to a height 14 of the assembly 1 in axial direction 15 and in the area of an end face 16 of the first green compact components 5 and/or in the area of an end face 17 of the second green compact component 6. The two end faces 15, 17 thereby point in axial direction 15.

In the region of the end faces 15 and/or 17 the at least one web 8 can be formed directly adjoining the end faces 15 and/or 17 (whereby the at least one web 8 forms part of the end faces 15 and/or 17) or is spaced apart from the end faces 15 and/or 17, wherein a distance 18 between the end faces 15 and/or 17 and an end face 19 of the at least one web is between 0% and 20% (excluding 0%) of the height 14 of the assembly 1 in axial direction 15.

Furthermore, a web height 20 of the at least one web 8 in axial direction 15 can be between 5% and 30% of the height 14 of the assembly 1 in axial direction 15. The web height 20 conforms essentially to the mechanical requirements for the strength of the connection of the two green compact components 5, 6, whereby the strength should not be so great than the subsequent separation of the two components 2, 3 is made much more difficult. The exact web height which is preferable for a specific assembly 1 can be determined from a small number of trials.

In the configuration with a plurality of webs 8 all of the latter can have the same web height 20. It is also possible however for at least one of the plurality of webs to have a different web height 10 from the web height 20 of the remaining webs 8. In one variation it is also possible that in the design with only one web 8, the latter has at least one area over its periphery 11, which is narrower or thicker than the remaining areas of the web 8. However, even with a plurality of webs 8 at least one web 8 can be designed to have at least one thickened part or tapering over its circumference 11 (as viewed in axial direction 15).

Furthermore, as shown in FIG. 2 in the design with a plurality of webs 8, all of the webs 8 can be designed to be at the same height (as viewed in axial direction 15). It is also possible however that at least one of the plurality of webs 8 is formed at a height which is different from the height of the remaining webs 8.

Preferably, only one predetermined breaking point is formed over the height 14 of the assembly 1 in axial direction 15. However, it is also possible to provide a plurality of predetermined breaking points, for example a plurality of webs 8, above one another in axial direction 15. Here for example at least one first web 8 can be designed as in FIG. 1 on or in the region of the end faces 16 and/or 19 and at least one further web in the region of the end faces of the components 2, 3 opposite the end faces 16, 19 in axial direction, whereby for the at least one further web the same can apply to the at least one web 8.

The phrase “end faces 16 and/or 19” are used above. This means that the two end faces 16, 19 need not necessarily be arranged in the same plane. Thus one of the two components 2 or 3 can have a different extension in the direction of the axial direction 15 than the second component 3 or 2.

With regard to the extension of the at least one web 8 in the direction of the periphery 11 the same applies as to the web height 20 in that the extension, which is advantageous for a specific assembly 1, can be determined by means of a small number of trials.

In FIG. 3 a further and possibly independent embodiment of the green compact 4 is shown for producing the assembly 1 according to FIG. 1, wherein for the same parts the same reference numerals and component names have been used as in FIG. 2. Therefore, to avoid unnecessary repetition reference is made to the detailed description of FIG. 2.

It should also be noted that the assembly 1 according to FIG. 1 is only one possible embodiment variant of the invention, although this is also the preferred embodiment variant.

Unlike the green compact according to FIG. 2 the connection of the first, inner green compact component 5 to the second, outer green compact component 6 is performed in this case not exclusively by at least one web 8 between the outer surface 10 of the first green compact component 5 and the inner surface 13 of the second green compact component 6, but the two green compact components 5, 6 are connected together at their end faces. In addition, at least one web 8 is provided which is formed both on the end face 16 of the first green compact component 5 and on the end face 19 of the second green compact component 6 and which bridges an intermediate space 21 between the two green compact components 5, 6.

As already explained above with reference to FIG. 2, one or more such webs 8 can be provided. In the case of a plurality of webs 8 the latter can be arranged distributed evenly around the periphery 11 of the assembly 1. The web or webs can all be configured to be of equal thickness or can be designed at least partly to have a different thickness. Reference is made to the above explanations.

If only one web 8 is formed the latter can also be in the form of a disk so that the web 8 covers the first, inner green compact component 5 at least almost completely, in particular fully.

Preferably, in all of the embodiment variants of the invention the two green compact components 5, 6 are arranged coaxially to one another and are connected together in this position so that the intermediate space 21 has a uniform gap width 22 over the whole periphery 11.

Furthermore, preferably all of the connecting elements, in particular the web or webs 8 are made from the powder from which the two green compact components 5, 6 are also made.

It is also possible within the scope of the invention for the assembly 1 to comprise more than two components 2, 3, which can be produced together, for example in that a further component is arranged inside the first component 2 or in that one of the components 2, 3 is configured to have multiple parts. In this case the more than two components 2, 3 can be connected until after the sintering, i.e. the latter are pressed together and then joined together by sintering.

The separation of the components 2, 3 after sintering can be performed by suitable machining methods, such as e.g. cutting or water jet cutting. Preferably however, the two components 2, 3 are separated by breaking or piercing or by turning. For example, the components 2, 3 produced with the green compact 4 according to FIG. 2 can be separated by breaking or by piercing. However, other methods are also known for separating the two components 2, 3, such as e.g. eroding, pressing, etc.

The remainder of the web or webs 8 left on the respective component 2, 3 can then be removed by machining, for example by turning. The components 2, 3 produced from the green compact 4 according to FIG. 3 can be separated simply by turning, and in this case the processing of the two components 2, 3 can be performed simultaneously, i.e. jointly.

After the separation the components 2 and/or 3 are calibrated if necessary and refined in the usual manner if necessary.

The components 2, 3 can however also be calibrated jointly, in particular partially calibrated, so that in this case the separation is performed after the calibration.

Furthermore, it is possible for the components 2, 3 to be separated by the calibration or during the calibration.

FIG. 4 shows a section consisting of an embodiment variant of the press mold 7 for producing the green compact 4 according to FIG. 2 in cross section.

The press mold 7 comprises a mold cavity consisting of a first mold cavity 23 and a second mold cavity 24. The first mold cavity 23 is used for receiving the sintering powder for producing the first green compact component 1, i.e. then the first component 3. The second mold cavity 24 is used for receiving the sintering powder for producing the second green compact component 1, i.e. then the second component 3. The two mold cavities 23, 24 are separated from one another by a mold wall 25.

In order to produce the at least one web 8 in the upper area, i.e. in the region of the filling opening for the sintering powder, the mold wall 25 has an opening 26, by means of which the two mold cavities 23, 24 are joined together. It is thus possible that on filling the press mold 7 with the sintering powder the area is also filled which in the green compact 4 forms the connection between the two green compact components 5, 6.

The precise number and form of the openings 26 conforms to the number of predetermined breaking points and their form in the green compact 4.

The at least one opening 26 can be open upwards in the direction of the filling opening. In this case the at least one web 8 directly adjoins the end faces 16 and/or 19 of the green compact components 5, 6, as described above in connection with FIG. 2.

If it is necessary to have a gap from end faces 16 and/or 19 the green compact components 5, 6, an extrusion punch 27, by means of which the inserted sintering powder is compacted, can have a projection 28 in the region of the at least one opening 26, which enters into the at least one opening 26 during the compaction of the sintering powder, but does not fill the latter completely, so that the at least one web 8 can be pressed. The height of the projection 28 is thus smaller than the height of the opening 26 in the same direction.

As the sintering powder is often compressed biaxially the press mold 7 can be formed alternatively or additionally on the lower side, i.e. the side opposite the filling opening, according to the aforementioned explanations.

FIG. 5 shows a section of an embodiment variant of the press mold 7 for producing the green compact 4 according to FIG. 3 in cross section.

In said press mold 7 the mold wall 25 between the two mold cavities 23, 24 does not have an opening. A base 29 with at least one depression 30 is provided for this, in which the webs 8 according to FIG. 3 are formed from the inserted sintering powder. Alternatively or in addition to this the extrusion punch 27 can also comprise at least one such depression 30.

By means of the at least one depression 30 the two mold cavities 23, 24 are connected together again.

The precise number and shape of the depressions 30 conforms to the number of predetermined breaking points and their form in the green compact 4.

If pressing is to be performed biaxially, i.e. the powder compaction, the base 29 is also in the form of an extrusion punch.

According to one embodiment variant of the method for producing the components 2, 3 it is possible that the first component is made from a first sintering powder and the second component is made from a second sintering powder, wherein the first sintering powder has a different composition than the second sintering powder.

It is also possible that the first component 2 and/or the second component 3 itself is/are produced from a plurality of different sintering powders, so that the first component 2 and/or the second component 3 consist in part from a metal material different from the rest of the first component 2 and/or the second component 3. In this way the load-bearing ability of the first component 2 and/or the second component 3 can be adapted more easily to specific requirements of the assembly 1.

Furthermore, it is possible that the first component 2 and/or the second component 3 themselves are made from a plurality of parts according to at least one of the aforementioned methods and the plurality of parts are only separated from one another after sintering.

The example embodiments show possible embodiment variants of the green compact 4 and the press mold 7 for the powder metallurgical production of an assembly 1, whereby it should be noted at this point that various different combinations of the individual embodiment variants are possible.

Thus it is possible for example that the at least one web 8 is formed both on the end face (as shown in FIG. 3) and between the outer surface 10 of the first green compact component 5 and the inner surface 13 of the second green compact component 6 (as shown in FIG. 2). Reference is made to the upper web 8 in FIG. 3 which shows this combination of the embodiment variants. Said web 8 comprises a shoulder 31 which projects into the intermediate space 21 between the two green compact components 5, 6. The corresponding press mold 7 for this is then a combination of the embodiment variants of the press mold 7 shown in FIGS. 4 and 5.

Said embodiment variant of the green compact 4 has the advantage that the two green compact components 5, 6 are joined together not only by the at least one web 8, but the two green compact components 5, 6 can also be supported on the at least one shoulder 31.

As a point of formality, it should be noted that for a better understanding of the structure of the green compact 4 and the press mold 7, the latter and their components have not been illustrated to scale in part and/or have been enlarged and/or reduced in size.

List of Reference Numerals 1 assembly 2 component 3 component 4 green compact 5 green compact component 6 green compact component 7 press mold 8 web 9 recess 10 surface 11 periphery 12 tapering 13 surface 14 height 15 direction 16 end face 17 end face 18 distance 19 end face 20 web height 21 intermediate space 22 gap width 23 mold cavity 24 mold cavity 25 mold wall 26 opening 27 pressing punch 28 projection 29 base 30 depression 31 shoulder 

1. A method for producing an assembly (1) comprising at least a first component (2) and a second component (3), the first component (2) being arranged at least partly inside the second component (3), and the first component (2) and the second component (3) being produced from at least one metal sintering powder according to a sintering method comprising the steps of powder pressing and sintering, wherein the first component (2) and the second component (3) comprising the metal sintering powder are pressed together in a mold to form a one-piece green compact (4) and the two components (2, 3) are only separated after sintering.
 2. The method as claimed in claim 1, wherein the first component (2) is connected to the second component (3) by at least one predetermined breaking point.
 3. The method as claimed in claim 2, wherein the predetermined breaking point is in the form of at least one web (8).
 4. The method as claimed in claim 3, wherein the at least one web (8) is formed between an outer surface (10) of the first component (2) and an inner surface (13) of the second component (3).
 5. The method as claimed in claim 3, wherein the at least one web (8) is formed off-center and in the area of one end face (17) of the first component (2) and/or in the area of one end face (19) of the second component (3).
 6. The method as claimed in claim 3, wherein a plurality of webs (8) are formed distributed evenly over a periphery (11) of the first component (2).
 7. The method as claimed in claim 6, wherein the plurality of webs (8) are formed at the same level.
 8. The method as claimed in claim 1, wherein the first component (2) and the second component (3) are joined together on their end faces.
 9. The method as claimed in claim 1, wherein the first component (2) is produced coaxially relative to the second component (3).
 10. The method as claimed in claim 1, wherein the first component (2) is separated from the second component (3) by breaking or by piercing or by turning.
 11. The method as claimed in claim 1, wherein the first component (2) is produced as a rotor and the second component (3) is produced as a stator of a pump.
 12. The method as claimed in claim 1, wherein the first component (2) is produced from a first sintering powder and the second component (3) is produced from a second sintering powder, wherein the first sintering powder has a different composition than the second sintering powder.
 13. A press mold (7) for producing a green compact (4) for an assembly (1) comprising at least a first component (2) and a second component (3), with a mold cavity for receiving at least one sintering powder, wherein the mold cavity comprises a first mold cavity (23) for the first component (2) and a second mold cavity (24) for the second component (3), wherein the first mold cavity (23) is separated from the second mold cavity (24) by at least one mold wall (25), and wherein the first mold cavity (23) is also surrounded at least partly by the second mold cavity (24), and wherein in the mold wall (25) separating the first mold cavity (23) from the second mold cavity (24) at least one opening (26) is formed, by means of which the first mold cavity (23) is connected to the second mold cavity (24).
 14. The press mold (7) for producing a green compact (4) for an assembly (1) comprising at least a first component (2) and a second component (3), with a mold cavity for receiving at least one sintering powder, and a pressing punch (27), wherein the mold cavity comprises a first mold cavity (23) for the first component (2) and a second mold cavity (24) for the second component (3), wherein the first mold cavity (23) is separated from the second cavity (24) by at least one mold wall (25), and wherein in a base area of the mold cavity and/or the pressing punch (27) at least one depression (30) is formed by means of which the first mold cavity (23) is connected to the second mold cavity (24). 